Effect of association-dissociation on the catalytic properties of glyceraldehyde 3-phosphate dehydrogenase

The enzymatic activity of d-glyceraldehyde 3-phosphate dehydrogenase depends nonlinearly on protein concentration in the range 3 × 10 −8 to 3 × 10 −6 m. With increasing enzyme concentrations the apparently hyperbolic substrate saturation curves turn into sigmoidal ones. From the kinetic and physicochemical data it is assumed that the enzyme exists as an equilibrium mixture of different oligomeric states. The system is found to be consistent with a model characterized by rapid equilibrium between monomer-dimer-tetramer, the tetramer being inactive, assuming identical intrinsic binding constants for the substrate in the monomer and in the dimer.